Low Distortion Mixer AD831

Transcription

1 a FEATURES Doubly-Balanced Mixer Low Distortion +2 dbm Third Order Intercept (IP3) + dbm 1 db Compression Point Low LO Drive Required: dbm Bandwidth MHz RF and LO Input Bandwidths 2 MHz Differential Current IF Output DC to >2 MHz Single-Ended Voltage IF Output Single or Dual Supply Operation DC Coupled Using Dual Supplies All Ports May Be DC Coupled No Lower Frequency Limit Operation to DC User-Programmable Power Consumption APPLICATIONS High Performance RF/IF Mixer Direct to Baseband Conversion Image-Reject Mixers I/Q Modulators and Demodulators PRODUCT DESCRIPTION The AD31 is a low distortion, wide dynamic range, monolithic mixer for use in such applications as RF to IF down conversion in HF and VHF receivers, the second mixer in DMR base stations, direct-to-baseband conversion, quadrature modulation and demodulation, and doppler-shift detection in ultrasound imaging applications. The mixer includes an LO driver and a low-noise output amplifier and provides both user-programmable power consumption and 3rd-order intercept point. The AD31 provides a +2 dbm third-order intercept point for dbm LO power, thus improving system performance and reducing system cost compared to passive mixers, by eliminating the need for a high power LO driver and its attendant shielding and isolation problems. The RF, IF, and LO ports may be dc or ac coupled when the mixer is operating from ± V supplies or ac coupled when operating from a single supply of 9 V minimum. The mixer operates with RF and LO inputs as high as MHz. The mixer s IF output is available as either a differential current output or a single-ended voltage output. The differential output is from a pair of open collectors and may be ac coupled via a transformer or capacitor to provide a 2 MHz output bandwidth. In down-conversion applications, a single capacitor connected across these outputs implements a low-pass filter to reduce harmonics directly at the mixer core, simplifying output FUNCTIONAL BLOCK DIAGRAM Low Distortion Mixer AD31 AN IFN IFP AP AD BIAS filtering. When building a quadrature-amplitude modulator or image reject mixer, the differential current outputs of two AD31s may be summed by connecting them together. An integral low noise amplifier provides a single-ended voltage output and can drive such low impedance loads as filters, Ω amplifier inputs, and A/D converters. Its small signal bandwidth exceeds 2 MHz. A single resistor connected between pins and FB sets its gain. The amplifier s low dc offset allows its use in such direct-coupled applications as direct-to-baseband conversion and quadrature-amplitude demodulation. The mixer s SSB noise figure is.3 db at MHz using its output amplifier and optimum source impedance. Unlike passive mixers, the AD31 has no insertion loss and does not require an external diplexer or passive termination. A programmable-bias feature allows the user to reduce power consumption, with a reduction in the 1 db compression point and third-order intercept. This permits a tradeoff between dynamic range and power consumption. For example, the AD31 may be used as a second mixer in cellular and two-way radio base stations at reduced power while still providing a substantial performance improvement over passive solutions. PRODUCT HIGHLIGHTS 1. dbm LO Drive for a +2 dbm Output Referred Third Order Intercept Point 2. Single-Ended Voltage Output 3. High Port-to-Port Isolation. No Insertion Loss. Single or Dual Supply Operation..3 db Noise Figure REV. B Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Analog Devices, Inc., 199 One Technology Way, P.O. Box 9, Norwood. MA 22-9, U.S.A. Tel: 1/329- Fax: 1/32-3

2 AD31 SPECIFICATIONS Parameter Conditions Min Typ Max Units RF INPUT Bandwidth dbm Signal Level, IP3 +2 dbm MHz. MHz IF and High Side Injection See Figure 1 1 db Compression Point dbm Common-Mode Range ±1 V Bias Current DC Coupled µa DC Input Resistance Differential or Common Mode 1.3 kω Capacitance 2 pf IF PUT Bandwidth Single-Ended Voltage Output, 3 db Level = dbm, R L = Ω 2 MHz Conversion Gain Terminals and Connected db Output Offset Voltage DC Measurement; LO Input Switched ±1 1 + mv Slew Rate 3 V/µs Output Voltage Swing R L = Ω, Unity Gain ±1. V Short Circuit Current ma LO INPUT Bandwidth dbm Input Signal Level MHz. MHz IF and High Side Injection Maximum Input Level 1 +1 V Common-Mode Range 1 +1 V Minimum Switching Level Differential Input Signal 2 mv p-p Bias Current DC Coupled 1 µa Resistance Differential or Common Mode Ω Capacitance 2 pf ISOLATION BETWEEN PORTS LO to RF LO = MHz, R S = Ω,. MHz IF db LO to IF LO = MHz, R S = Ω,. MHz IF 3 db RF to IF RF = MHz, R S = Ω,. MHz IF db DISTORTION AND NOISE LO = dbm, f = MHz, IF =. MHz 3rd Order Intercept Output Referred, ± mv LO Input 2 dbm 2rd Order Intercept Output Referred, ± mv LO Input 2 dbm 1 db Compression Point R L = Ω, R BIAS = dbm Noise Figure, SSB Matched Input, RF = MHz, IF =. MHz.3 db Matched Input, RF = 1 MHz, IF =. MHz 1 db POWER SUPPLIES Recommended Supply Range Dual Supply ±. ±. V Single Supply 9 11 V Quiescent Current 1 For Best 3rd Order Intercept Point Performance 12 ma BIAS Pin Open Circuited NOTES 1 Quiescent current is programmable. Specifications subject to change without notice. (T A = +2 C and V S = V unless otherwise noted; all values in dbm assume load.) 2 REV. B

3 AD31 ABSOLUTE MAXIMUM RATINGS 1 Supply Voltage ±V S ±. V Input Voltages RFHI, RFLO ±3 V LOHI, LOLO ±1 V Internal Power Dissipation mw Operating Temperature Range AD31A C to + C Storage Temperature Range C to +1 C Lead Temperature Range (Soldering sec) C NOTES 1 Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. 2 Thermal Characteristics: 2-Pin PLCC Package: θ JA = 1 C/Watt; θ JC = 2 C/Watt. Note that the θ JA = 1 C/W value is for the package measured while suspended in still air; mounted on a PC board, the typical value is θ JA = 9 C/W due to the conduction provided by the AD31 s package being in contact with the board, which serves as a heat sink. ORDERING GUIDE Temperature Package Package Model Range Description Option AD31AP C to + C 2-Lead PLCC P-2A PIN CONFIGURATION 2-Lead PLCC AN IFN IFP AD31 TOP VIEW (Not to Scale) 9 11 PIN DESCRIPTION Pin Mnemonic Description 1 Positive Supply Input 2 IFN Mixer Current Output 3 AN Amplifier Negative Input Ground Negative Supply Input RF Input RF Input Negative Supply Input 9 Positive Supply Input Local Oscillator Input 11 Local Oscillator Input 12 Positive Supply Input 13 Ground 1 BIAS Bias Input 1 Negative Supply Input 1 Amplifier Output 1 Amplifier Feedback Input 1 Amplifier Output Common 19 AP Amplifier Positive Input 2 IFP Mixer Current Output AP BIAS CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as V readily accumulate on the human body and test equipment and can discharge without detection. Although the AD31 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality. WARNING! ESD SENSITIVE DEVICE REV. B 3

4 AD31 Typical Characteristics 3 THIRD ORDER INTERCEPT dbm SECOND ORDER INTERCEPT dbm Figure 1. Third-Order Intercept vs. Frequency, IF Held Constant at. MHz Figure. Second-Order Intercept vs. Frequency ISOLATION db 3 2 ISOLATION db Figure 2. IF-to-RF Isolation vs. Frequency Figure. LO-to-RF Isolation vs. Frequency ISOLATION db x LO-to-IF 3 x LO-to-IF LO ISOLATION db 3 3 x RF-to-IF 2 x RF-to-IF RF-to-IF 3 x RF-to-IF 2 x RF-to-IF RF-to-IF 2 Figure 3. LO-to-IF Isolation vs. Frequency Figure. RF-to-IF Isolation vs. Frequency REV. B

5 AD dB PRESSION POINT dbm 2 GAIN ERROR db Figure. 1 db Compression Point vs. Frequency, Gain = 1 Figure. Gain Error vs. Frequency, Gain = dB PRESSION POINT dbm 2 1dB PRESSION POINT dbm Figure. 1 db Compression Point vs. RF Input, Gain = 2 Figure db Compression Point vs. Frequency, Gain = 2 11 THIRD ORDER INTERCEPT dbm MIXER PUT TRANSFORMER COUPLED PER FIGURE 1 MIXER PLUS AMPLIFIER, G = 1 1dB PRESSION POINT dbm 9 LO LEVEL = dbm IF =.MHz V S = V V S = 9V Figure 9. Third-Order Intercept vs. Frequency, LO Held Constant at 21 MHz Figure 12. Input 1 db Compression Point vs. Frequency, Gain = 1, 9 V Single Supply REV. B

6 AD31 Typical Characteristics 3 12 INPUT RESISTANCE. THIRD ORDER INTERCEPT dbm 2 2 LO LEVEL = dbm IF =.MHz f = 2kHz V S = 9V V S = V INPUT RESISTANCE Ohms 2 INPUT CAPACITANCE INPUT CAPACITANCE pf Figure 13. Input Third Order Intercept, 9 V Single Supply Figure 1. Input Impedance vs. Frequency, Z IN = R C SECOND ORDER INTERCEPT dbm V S = V V S = 9V LO LEVEL = dbm IF =.MHz f = 2kHz NOISE FIGURE db Figure 1. Input Second Order Intercept, 9 V Single Supply Figure 1. Noise Figure vs. Frequency, Matched Input REV. B

7 AD31 THEORY OF OPERATION The AD31 consists of a mixer core, a limiting amplifier, a low noise output amplifier, and a bias circuit (Figure 1). The mixer s RF input is converted into differential currents by a highly linear, Class A voltage-to-current converter, formed by transistors Q1, Q2 and resistors R1, R2. The resulting currents drive the differential pairs Q3, Q and Q, Q. The LO input is through a high gain, low noise limiting amplifier that converts the dbm LO input into a square wave. This square wave drives the differential pairs Q3, Q and Q, Q and produces a high level output at IFP and IFN consisting of the sum and difference frequencies of the RF and LO inputs and a series of lower level outputs caused by odd harmonics of the LO frequency mixing with the RF input. An on-chip network supplies the bias current to the RF and LO inputs when these are ac coupled; this network is disabled when the AD31 is dc coupled. When the integral output amplifier is used, pins IFN and IFP are connected directly to pins AFN and AFP; the on-chip load resistors convert the output current into a voltage that drives the output amplifier. The ratio of these load resistors to resistors R1, R2 provides nominal unity gain ( db) from RF to IF. The expression for the gain, in decibels, is 1 π G db = 2 log Equation 1 π 2 2 where is the amplitude of the fundamental component of a square wave π 1 is the conversion loss 2 π is the small signal dc gain of the AD31 when the LO input 2 is driven fully positive or negative. 1 AP 19 3 AN 2Ω 2Ω IFP 2 2 IFN 1mA TYP 1mA TYP BIAS A O 1 LOCAL OSCILLATOR INPUT RF INPUT 11 Q3 LIMITING AMPLIFIER Q2 Q R 1kΩ R1 2Ω Q R 1kΩ R2 2Ω Q Q1 kω kω CURRENT MIRROR BIAS 1 1 BIAS BIAS CURRENT Q R3 2Ω 3Ω 3mA TYP 12mA TYP 2mA TYP Figure 1. Simplified Schematic Diagram REV. B

8 AD31 The mixer has two open-collector outputs (differential currents) at pins IFN and IFP. These currents may be used to provide nominal unity RF-to-IF gain by connecting a center-tapped transformer (1:1 turns ratio) to pins IFN and IFP as shown in Figure 1. IF PUT MCLT-1H OS 1 IFP 2 2 IFN 1mA TYP 1mA TYP Low-Pass Filtering A simple low-pass filter may be added between the mixer and the output amplifier by shunting the internal resistive loads (an equivalent resistance of about 1 Ω with a tolerance of 2%) with external capacitors; these attenuate the sum component in a down-conversion application (Figure 2). The corner frequency of this one-pole low-pass filter (f = (2 π RC F ) 1 ) should be placed about an octave above the difference frequency IF. Thus, for a MHz IF, a 3 db frequency of MHz might be chosen, using C F = (2 π 1 Ω MHz) 1 2 pf, the nearest standard value. C F = 1 = 2 π f R 1 9. f LOCAL OSCILLATOR INPUT RF INPUT 11 Q3 LIMITING AMPLIFIER Q2 Q R 1kΩ R1 2Ω Q R 1kΩ R2 2Ω Q Q1 kω kω C F C F AN IFN IFP AP 1 1 BIAS BIAS CURRENT Q R3 2Ω 3mA TYP Figure 1. Connections for Transformer Coupling to the IF Output Programming the Bias Current Because the AD31 s RF port is a Class-A circuit, the maximum RF input is proportional to the bias current. This bias current may be reduced by connecting a resistor from the BIAS pin to the positive supply (Figure 19). For normal operation, the BIAS pin is left unconnected. For lowest power consumption, the BIAS pin is connected directly to the positive supply. The range of adjustment is ma for normal operation to ma total current at minimum power consumption. AD BIAS 1 Figure 2. Low-Pass Filtering Using External Capacitors Using the Output Amplifier The AD31 s output amplifier converts the mixer core s differential current output into a single-ended voltage and provides an output as high as ±1 V peak into a Ω load (+ dbm). For unity gain operation (Figure 21), the inputs AN and AP connect to the open-collector outputs of the mixer s core and connects to. AN IFN IFP AP 1 AN IFN IFP AP AD BIAS kΩ OS NOTE ADDED RESISTOR AD BIAS 1 IF PUT Figure 19. Programming the Quiescent Current Figure 21. Output Amplifier Connected for Unity Gain Operation REV. B

9 AD31 For gains other than unity, the amplifier s output at is connected via an attenuator network to ; this determines the overall gain. Using resistors R1 and R2 (Figure 22), the gain setting expression is G db = 2 log AD31 R1+ R2 R2 AN IFN IFP AP BIAS 1 Equation 2 R2 R1 IF PUT Figure 22. Output Amplifier Feedback Connections for Increasing Gain Driving Filters The output amplifier can be used for driving reverse-terminated loads. When driving an IF bandpass filter (BPF), for example, proper attention must be paid to providing the optimal source and load terminations so as to achieve the specified filter response. The AD31 s wideband highly linear output amplifier affords an opportunity to increase the RF-to-IF gain to compensate for a filter s insertion and termination losses. Figure 23 indicates how the output amplifier s low impedance (voltage source) output can drive a doubly-terminated bandpass filter. The typical db of loss ( db of insertion loss and db due to the reverse-termination) be made up by the inclusion of a feedback network that increases the gain of the amplifier by db ( 3.12). When constructing a feedback circuit, the signal path between and should be as short as possible. AN IFN IFP AP 1 R2 1.1Ω 1 R1 1Ω 1 AD BIAS 1 R T BPF R T IF PUT Figure 23. Connections for Driving a Doubly-Terminated Bandpass Filter Higher gains can be achieved, using different resistor ratios, but with concomitant reduction in the bandwidth of this amplifier (Figure 2). Note also that the Johnson noise of these gain-setting resistors, as well as that of the BPF terminating resistors, is ultimately reflected back to the mixer s input; thus they should be as small as possible, consistent with the permissible loading on the amplifier s output. 1dB PRESSION POINT dbm 12 2 G = 1 G = 2 G = Figure 2. Output Amplifier 1 db Compression Point for Gains of 1, 2, and (Gains of db, db, and 12 db, Respectively) REV. B 9

10 AD31 APPLICATIONS Careful component selection, circuit layout, power supply decoupling, and shielding are needed to minimize the AD31 s susceptibility to interference from radio and TV stations, etc. In bench evaluation, we recommend placing all of the components in a shielded box and using feedthrough decoupling networks for the supply voltage. Circuit layout and construction are also critical, since stray capacitances and lead inductances can form resonant circuits and are a potential source of circuit peaking, oscillation, or both. Dual-Supply Operation Figure 2 shows the connections for dual supply operation. Supplies may be as low as ±. V but should be no higher than ±. V due to power dissipation. The RF input to the AD31 is shown connected by an impedance matching network for an assumed source impedance of Ω. Figure 1 shows the input impedance of the AD31 plotted vs. frequency. The input circuit can be modeled as a resistance in parallel with a capacitance. The 2 pf capacitors (C F ) connected from IFN and IFP to provide a low-pass filter with a cutoff frequency of approximately MHz in downconversion applications (see the Theory of Operation section of this data sheet for more details). The LO input is connected single-ended because the limiting amplifier provides a symmetric drive to the mixer. To minimize intermodulation distortion, connect pins and by the shortest possible path. The connections shown are for unity-gain operation. At LO frequencies less than MHz, the AD31 s LO power may be as low as 2 dbm for satisfactory operation. Above MHz, the specified LO power of dbm must be used. C F 2pF C F 2pF AN IFN IFP AP 1 1.1Ω 1 RF INPUT C1 C2 V 1Ω 1 R T BPF IF PUT L1 AD31 1 BIAS 1 NC V R T V Ω LO INPUT dbm Figure 2. Connections for ± V Dual-Supply Operation Showing Impedance Matching Network and Gain of 2 for Driving Reverse-Terminated IF Filter REV. B

11 AD31 Single Supply Operation Figure 2 is similar to the dual supply circuit in Figure 19. Supplies may be as low as 9 V but should not be higher than 11 V due to power dissipation. As in Figure 19, both the RF and LO ports are driven single-ended and terminated. In single supply operation, the terminal is the ground reference for the output amplifier and must be biased to 1/2 the supply voltage, which is done by resistors R1 and R2. The pin must be ac-coupled to the load. +9V 2pF 2pF AN IFN IFP AP 1 1 kω kω R2 1.1Ω R1 1Ω RF INPUT C1 L1 C2 AD BIAS 1 NC R T C C IF PUT +9V Ω +9V LO INPUT dbm Figure 2. Connections for +9 V Single-Supply Operation REV. B 11

12 AD31 Connections Quadrature Demodulation Two AD31 mixers may have their RF inputs connected in parallel and have their LO inputs driven in phase quadrature (Figure 2) to provide demodulated in-phase (I) and quadrature (Q) outputs. The mixers inputs may be connected in parallel and a single termination resistor used if the mixers are located in close proximity on the PC board. C F C F AN IFN IFP AP 1 1 V 1 DEMODULATED QUADRATURE PUT AD31 1 BIAS 1 NC V V Ω IF INPUT 1.1Ω LO INPUT AT 9 dbm C F C F AN IFN IFP AP 1 1 V 1 DEMODULATED IN-PHASE PUT AD31 1 BIAS 1 NC V V Ω LO INPUT AT dbm Figure 2. Connections for Quadrature Demodulation 12 REV. B

13 AD31 Table I. AD31 Mixer Table,. V Supplies, LO = 9 dbm LO Level 9. dbm, LO Frequency 13. MHz, Data File imdtb1 RF Level. dbm, RF Frequency 12 MHz Temperature Ambient Dut Supply ±. V OS Current 9 ma EG Current 91 ma Intermodulation Table RF harmonics (rows) LO harmonics (columns). First row absolute value of nrf-mlo, and second row is the sum Table II. AD31 Mixer Table, V Supplies, LO = 9 dbm LO Level 9. dbm, LO Frequency 13. MHz, Data File imdtb132 RF Level. dbm, RF Frequency 12 MHz Temperature Ambient Dut Supply ±. V OS Current 2 ma EG Current 2 ma Intermodulation table RF harmonics (rows) LO harmonics (columns). First row absolute value of nrf-mlo, and second row is the sum REV. B 13

14 AD31 Table III. AD31 Mixer Table, 3. V Supplies, LO = 2 dbm LO Level 2. dbm, LO Frequency 13. MHz, Data File G1T1K 1 RF Level. dbm, RF Frequency 12 MHz Temperature Ambient Dut Supply ±3. V OS Current ma EG Current ma Intermodulation Table RF harmonics (rows) LO harmonics (columns). First row absolute value of nrf-mlo, and second row is the sum Table IV. AD31 Mixer Table, V Supplies, 1 k Bias Resistor, LO = 2 dbm LO Level 2. dbm, LO Frequency 13. MHz, Data File G1T1K 31 RF Level. dbm, RF Frequency 12 MHz Temperature Ambient Dut Supply ±3. V OS Current 9 ma EG Current 1 ma Intermodulation table RF harmonics (rows) LO harmonics (columns). First row absolute value of nrf-mlo, and second row is the sum REV. B

15 AD31 HP 32A PROGRAMMABLE POWER SUPPLY HP 32A PROGRAMMABLE POWER SUPPLY HP B SYNTHESIZED SIGNAL GENERATOR V MCL ZFSC-2-1 BINER AD31 PER FIGURE 2 HP 1E SPECTRUM ANALYZER HP A SYNTHESIZED SIGNAL GENERATOR LO HP 992 IEEE CONTROLLER HP 9121 DISK DRIVE FLUKE 2A SYNTHESIZED SIGNAL GENERATOR IEEE- BUS Figure 2. Third-Order Intercept Characterization Setup HP 32A PROGRAMMABLE POWER SUPPLY HP 32A PROGRAMMABLE POWER SUPPLY HP B SYNTHESIZED SIGNAL GENERATOR MCL ZFSC-2-1 RF V AD31 PER FIGURE 2 IF HP B SYNTHESIZED SIGNAL GENERATOR LO MCL ZFSC-2-1 USED FOR IF TO RF, LO LO TO RF MOVE SPECTRUM ANALYZER FOR IF MEASUREMENTS HP 1E SPECTRUM ANALYZER HP B SYNTHESIZED SIGNAL GENERATOR Figure 29. IF to RF Isolation Characterization Setup REV. B 1

16 AD31 LINE DIMENSIONS Dimensions shown in inches and (mm). 2-Lead PLCC (P-2A). (1.21).2 (1.). (1.2) BSC.2 (.) R. (1.21).2 (1.) 3 9 PIN 1 IDENTIFIER TOP VIEW. (1.2).2 (1.) (9.) SQ.3 (.9).39 (.2) SQ.3 (9.) 1 1. (.).1 (.19).1 (2.9). (2.1).2 (.3).1 (.3) C19a /9.21 (.3).13 (.33).33 (.3).29 (.3).32 (.1).2 (.). (1.1).2 (.) PRINTED IN U.S.A. C19a /9 1 REV. B